Flexibility is definitely the name of the game but, except for the very nervous, I think it's important that they get a feel for various aspects of flying - not just EOC. I would normally brief primary EOC, the importance of attitude ("take a mental photograph") and the basics of medium turns (but explain that I'll be using the rudder for them on this trip) - with meet'n'greet this takes about 10 mins using a model (no writing on whiteboards!).
I don't agree with the idea of giving a full chalk'n'talk Ex4 brief unless it really is the first trip of a course. I also don't like the idea of someone else doing the briefing - this is an important time to build a relationship with the stude, not just a formality to be gone through.
In the aircraft I show them how to taxi (whilst doing the taxi checks) and then get them to taxi to the hold. At the hold I explain the checks as I do them. I'll probably get them to do the take-off, then takeover for the checks and to demo the climb attitude and primary EOC, then hand control back so they can practice primary EOC in the climb. Once settled I'll talk them through turns and (usually) climbs/descents, local landmarks (house, airfield, etc), then get them to fly back to the airfield. At some time they'll make an R/T call and there'll be some laughter about something. The importance of Lookout and Attitude are emphasised at every stage.
Afterwards: a brief recap, explain how to take it further, sign the certificate and bid farewell. This is all easily done as a 30 min trip in a 60 min slot.